The purification and characterization of S-adenosylmethionine (AdoMet) synthetase (EC 2.5.1.6) from yeast is currently in progress. We have been able to demonstrate the existence of two molecular species of AdoMet synthetase which exhibit differences in chromatographic behavior and electrophoretic mobility. These two species of AdoMet synthetase have identical molecular weight, approximately 110,000 when estimated by Sephadex G-150. Both forms of the enzyme catalyze the cleavage of inorganic tripolyphosphate. AdoMet synthetase is totally dependent upon added AdoMet for its tripolyphosphatase activity, whereas the tripolyphosphatase activity of AdoMet synthetase I is active without addition of exogenous AdoMet although in its presence, its activity is significantly higher. BIBLIOGRAPHIC REFERENCES: Chiang, P.K. and Cantoni, G.L.: Activation of methionine for transmethylation. Purification of the S-adenosylmethionine synthetase of baker's yeast and its separation into two forms. J. Biol. Chem. 252: 4506-4513, 1977. Cantoni, G.L.: Formyl metabolism. Encyclopedia of Chemistry, V. Florence, Italy, USES Publishers, 1976, pp. 527-532.